1. Field of the Invention
The present invention relates to a disk apparatus for use in, e.g., a magnetic recording system, optical recording system, or magneto-optical recording system, a cover and a case of the disk apparatus, and a gasket for sealing the portion between the cover and case.
2. Description of the Related Art
Generally, a gasket is sandwiched between a case of a disk apparatus and a cover for covering the case. This gasket blocks the flow of air between the case and cover, thereby sealing the portion between them.
This gasket is a molded product formed using an elastic material and having a frame-like shape corresponding to the shape of that frame surface of the case, which faces the cover.
As this gasket material, a fluorine-based resin and hydrocarbon-based elastic materials such as EPDM can be used.
A fluorine-based resin has characteristics unique to the material. That is, surface adsorption contamination by an impurity gas from the environment is little, and the water vapor blocking capability, chemical resistance, and weather resistance are high. Also, since the molding temperature is high, a molded part having only a small amount of an impurity gas component can be formed.
However, molding must be performed at high temperatures, so that a life of a die can become short and the cost of molding can be higher. Also, since the material flowability is low and so is the moldability, a complicated shape or fine shape is difficult to mold. In addition, the specific gravity is large.
On the other hand, the water blocking capability of EPDM is slighter lower than that of the fluorine-based resin. However, the cost of molding of this EPDM is lower, has high moldability, and allows a complicated shape or fine shape to be molded at low molding temperatures. EPDM is also superior to the fluorine-based resin in specific gravity. Accordingly, this EPDM is often used.
Unfortunately, EPDM has the disadvantage that it is susceptible to adsorption contamination by a siloxane-based gas. Therefore, a siloxane-based gas present in the production environment and storage environment is easily adsorbed by an EPDM raw material and molded EPDM product. If such EPDM product is used as a part of a disk apparatus, the siloxane-based gas is released as an outgas component into the apparatus. The released siloxane-based gas deposits in undesired portions in the apparatus, e.g., a portion between a read/write element of a head and the surface of a disk medium and in a portion surrounding that portion. The deposited gas slides with the head and causes a defect, e.g., varies the floating posture of the head, thereby lowering the reliability of the disk apparatus.
Furthermore, hydrocarbon-based oil for hardness adjustment is added to a gasket using a hydrocarbon-based elastic material such as EPDM. This oil is extracted by a cleaning agent or organic solvent used in gasket cleaning or disk apparatus cleaning, and readily remains as a residue around the gasket. This residue may transfer to and contaminate the assembly environment, jig, and peripheral apparatus of the magnetic disk apparatus, thereby causing functional defects of various parts.
To prevent this, Jpn. Pat. Appln. KOKAI Publication No. 2000-344987, for example, proposes the use of a mixture of fluorine rubber and non-fluorine rubber, e.g., silicone rubber and acrylic rubber, as a gasket. However, this mixture contains a large amount of a siloxane-based organic gas component as an impurity, and the acrylic rubber is susceptible to adsorption contamination by siloxane from the environment. Therefore, the generation of outgas and the extraction of oil cannot be well prevented.